Medial smooth muscle cell (SMC) proliferation is a central event in hypoxic pulmonary artery remodeling. We hypothesize that hypoxia directly initiates a series of events in pulmonary artery SMC (PASMC) that lead to proliferation. We wish to characterize elements of this signaling cascade. We aim to: (1) Investigate the role of mitogen activated protein kinases (MAPK) by measuring MAPK phosphorylation in hypoxic PASMC, and by inhibition of MAPK pathways. (2) Clarify whether reactive oxygen species (ROS) or heme-like proteins play a role in the signaling pathway, by measuring intracellular ROS in hypoxic and normoxic PASMC, studying the effect of antioxidants on hypoxic PASMC proliferation, defining the specific RO involved, and also by studying the effect of CO, NO and CN. (3) Identify transcription factors (TFs) activated by hypoxia in PASMC. We hypothesize that GATA-4, HIF-1 and AP-1 are downstream effectors in this pathway. We will study DNA binding activity of these TFs in hypoxic PASMC by gel shift assay, study the effect of neutralizing these TFs on hypoxia-induced proliferation and screen for activation of unknown TFs by hypoxia, by studying the nuclear proteome of hypoxic PASMC. Understanding the mechanisms of hytpoxic remodeling will lead to novel therapeutic strategies for pulmonary hypertension.